Answers

A:

As per user manual it says "Calibrate the instrument before each use if possible. Especially if the meter has not been used for a long period of time"

To calibrate the 407732, an external calibrator that can provide a 94.0dB signal at 1 kHz is required in addition to a small screw-driver.Newark order code #27K9782 (407744 ) 94dB Sound Calibratorand #27K9791 (407766 ) 94/114dB Sound Calibrator

Refer user manual and product page link for more details:http://www.extech.com/instruments/resources/manuals/407732_UM.pdfhttp://www.extech.com/instruments/product.asp?catid=18&prodid=234